**Course Title:** Ruby Programming: From Basics to Advanced Techniques **Section Title:** Advanced Rails: Routing and Views **Topic:** Handling form submissions and validations Handling form submissions and validations is an essential aspect of building robust and user-friendly web applications with Ruby on Rails. In this topic, we'll explore how to handle form data, validate user input, and display errors in a Rails application. **Form Helpers in Rails** Before diving into form submissions and validations, let's take a look at how Rails provides form helpers to make building forms easier. Rails provides two form helpers: `form_for` and `form_tag`. `form_for` is used for model-backed forms, which are forms that interact with a specific model. This helper automatically generates the form fields based on the model's attributes. ```ruby # Using form_for for a User model <%= form_for @user do |form| %> <%= form.label :name %> <%= form.text_field :name %> <%= form.submit %> <% end %> ``` On the other hand, `form_tag` is used for non-model-backed forms, such as a simple contact form. ```ruby # Using form_tag for a non-model-backed form <%= form_tag('/contact', method: 'post') do %> <%= label_tag :name %> <%= text_field_tag :name %> <%= submit_tag 'Submit' %> <% end %> ``` **Handling Form Submissions** Handling form submissions involves processing the form data sent by the user and saving it to the database or performing some other action. To handle form submissions, you need to define a route for the form submission. ```ruby # Define a route for the form submission post '/users', to: 'users#create' ``` Next, create a controller action that handles the form submission. In this action, you can validate the user input, save the data to the database, and redirect the user to a success page. ```ruby # Handling form submission in the users controller class UsersController < ApplicationController def create @user = User.new(user_params) if @user.save redirect_to @user, notice: 'User created successfully!' else render 'new' end end private def user_params params.require(:user).permit(:name, :email) end end ``` **Validations** Validations are used to ensure that the user input is valid and meets the requirements of the application. Rails provides several built-in validations that you can use in your models. ```ruby # Using validations in the User model class User < ApplicationRecord validates :name, presence: true validates :email, format: { with: /\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\z/ } end ``` You can also use custom validations to validate complex logic. ```ruby # Using custom validations in the User model class User < ApplicationRecord validate :password_length private def password_length if password.length < 8 errors.add(:password, 'Password must be at least 8 characters') end end end ``` **Displaying Errors** Displaying errors is an essential part of building user-friendly forms. Rails provides several ways to display errors. ```html # Displaying errors using the flash message <% if flash[:error] %> <div class="alert alert-danger"> <%= flash[:error] %> </div> <% end %> ``` You can also use the `error_messages` helper to display errors. ```ruby # Displaying errors using the error_messages helper <%= form_for @user do |form| %> <%= form.error_messages %> <%= form.label :name %> <%= form.text_field :name %> <%= form.submit %> <% end %> ``` **Conclusion** In this topic, we've covered the basics of handling form submissions and validations in a Rails application. We've explored how to use form helpers to build forms, handle form submissions, validate user input, and display errors. **Additional Resources** * [Active Record Validations](https://guides.rubyonrails.org/active_record_validations.html) * [Form Helpers](https://apidock.com/rails/v5.2.3/ActionView/Helpers/FormHelper) **Questions or Need Help?** If you have any questions or need help with this topic, feel free to leave a comment below.